Cognitive ability may decline as a normal consequence of aging or as a consequence of a central nervous disorder.
For example, a significant population of elderly adults experiences a decline in cognitive ability that exceeds what is typical in normal aging. Such age-related loss of cognitive function is characterized clinically by progressive loss of memory, cognition, reasoning, and judgment. Mild Cognitive Impairment (MCI), Age-Associated Memory Impairment (AAMI), Age-Related Cognitive Decline (ARCD) or similar clinical groupings are among those related to such age-related loss of cognitive function. According to some estimates, there are more than 16 million people with AAMI in the U.S. alone (Barker et al., 1995), and MCI is estimated to affect 5.5-7 million in the U.S. over the age of 65 (Plassman et al., 2008).
Cognitive impairment is also associated with other central nervous system (CNS) disorders, such as dementia, Alzheimer's Disease (AD), prodromal AD, post traumatic stress disorder (PTSD), schizophrenia, bipolar disorder (in particular, mania), amyotrophic lateral sclerosis (ALS), cancer-therapy-related cognitive impairment, mental retardation, Parkinson's disease (PD), autism spectrum disorders, fragile X disorder, Rett syndrome, compulsive behavior, and substance addiction.
There is, therefore, a need for effective treatment of cognitive impairment associated with central nervous system (CNS) disorders and to improve cognitive function in patients diagnosed with, for example, age-related cognitive impairment, MCI, amnestic MCI, AAMI, ARCD, dementia, AD, prodromal AD, PTSD, schizophrenia or bipolar disorder (in particular, mania), amyotrophic lateral sclerosis (ALS), cancer-therapy-related cognitive impairment, mental retardation, Parkinson's disease (PD), autism spectrum disorders, fragile X disorder, Rett syndrome, compulsive behavior, and substance addiction and similar central nervous system (CNS) disorders with cognitive impairment or at risk of developing them.
GABAA receptors (GABAA R) are pentameric assemblies from a pool of different subunits (α1-6, β1-3, γ1-3, δ, ε, π, θ) that form a Cl-permeable channel that is gated by the neurotransmitter γ-aminobutyric acid (GABA). Various pharmacological effects, including anxiety disorders, epilepsy, insomnia, pre-anesthetic sedation, and muscle relaxation, are mediated by different GABAA subtypes.
Various studies have demonstrated that reduced GABA signaling is linked to various CNS disorders with cognitive impairment. In particular, the α5-containing GABAA Rs, which are relatively sparse in the mammalian brain, play a role in modifying learning and memory. Previous studies demonstrated a reduction of hippocampal expression of the α5 subunit of the GABAA receptor in rats with age-related cognitive decline (see International Patent Publication WO 2007/019312). Such results suggest that upregulation of α5-containing GABAA R function may be effective in the treatment of cognitive impairment associated with said CNS disorders.
Thus, there is a need for positive allosteric modulators of α5-containing GABAA R that are useful in therapeutic preparations for the treatment of cognitive impairment associated with said CNS disorders.